ChiP assay band in negative control

I have been doing ChiP assay using a kit from Upstate, millipore. I completed the entire procedure and did PCR for GAPDH promoter sequence with positive control (RNA Pol II antibody) and negative control (Mouse IgG). Surprisingly i got a band in both positive and negative . The band was fainter in negative, but then there was a distinct band after PCR.